This invention relates generally to apparatus for detecting the passage of objects composed at least in part of metallic or magnetic materials, including iron and steel, and more particularly to an improved configuration of magnetic field and sending coils for such detecting systems.
This invention is an improvement upon the metal detecting apparatus of the type using a magnetic detector for machinery having a magnetic field and generating means which results in magnetic fields which are essentially parallel to the direction of travel of material being fed into the machines. The orientation of these magnetic fields creates a distinct sensitivity pattern in the metal detecting action. The electrical signal from these existing detectors varies considerably with the orientation of the metal piece being sensed, because when the orientation of a piece of metal with a long narrow configuration is such that its principle axis is transverse to the magnetic lines of flux, the electrical signal is somewhat diminished. However, when the same shape of metal passes through the magnetic field with its principle axis orientation parallel to the lines of flux, that is, essentially spanning the gap between magnetic poles, the signal is strong. Such a variation results in a detection performance which varies with target orientation.
The foregoing illustrates limitations of the known prior art. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations as set forth above.
Accordingly, a suitable alternative is to use magnetic members which create multi-directional magnetic fields and corresponding sensing coils which sense all metal passing within the fields at approximately the same signal level without being severely diminished for any particular orientation.